Methods for fabricating composite structures with flanges having tethered corners

ABSTRACT

Methods for fabricating a composite structure with a flange having a tethered corner involving providing a composite structure forming tool including a first endplate and a second endplate and having a composite structure formed thereabout, applying at least one ply of barrier fibers about the composite structure adjacent to the first endplate of the composite structure forming tool, and wrapping at least one fiber tow about the barrier fibers.

TECHNICAL FIELD

Embodiments described herein generally relate to methods for fabricatingcomposite structures with flanges having tethered corners.

BACKGROUND OF THE INVENTION

In recent years composite materials have become increasingly popular foruse in a variety of aerospace applications because of their durabilityand relative lightweight. Although composite materials can providesuperior strength and weight properties, designing flanges on structuresfabricated from composite materials still remains a challenge.

Current flange lay-up processes can generally involve repeatedlyapplying plies, or layers, of fabric to a composite structure until aflange having the desired dimensions is obtained. One issue that canarise during this process is that when a second ply of fabric isapplied, it can cover the first ply of fabric, thereby making it nearlyimpossible to monitor the first ply to ensure its placement isunchanged. As a result, bridging of the fabric may occur.

Bridging is when the initial, or first, fabric ply pulls away from theflange corner and spans across the corner rather than remaining tightlyadhered thereto. Bridging may result in resin richness, which is anundesired agglomeration of excess resin beneath the first ply of fabricthat can locally weaken the laminate.

Bridging may be caused by any of several factors. For example, bridgingmay result from inadequately placing the initial fabric plies into thecorner of the flange such that as subsequent plies are applied duringlay-up the initial plies may be jostled causing bridging. Also,inadequately removing bulk from the fabric plies during layup can resultin an excess length of composite material, which can lead to bridgingduring the curing process. Additionally, bridging may result fromdifferences in thermal expansion of the tooling versus the fabric duringthe curing process.

Regardless of the cause, there is currently no way for operators toeasily monitor the initial fabric ply once it has been covered to helpensure that bridging is prevented and that the first ply of fabricremains adhered in the flange corner. The best current practice is toterminate the fabric plies at the corner to allow fabric slippage.However, this practice is generally only beneficial in addressing theissue of differences in thermal expansion during cure and does nothingto prevent bridging that occurs as a result of jostling or inadequatebulk removal.

Accordingly, it would be desirable to provide methods for fabricatingflanges that are less susceptible to bridging and the previouslydescribed fabrication concerns.

BRIEF DESCRIPTION OF THE INVENTION

Embodiments herein generally relate to methods for fabricating compositestructures with flanges having tethered corners comprising providing acomposite structure forming tool including a first endplate and a secondendplate and having a composite structure formed thereabout, applying atleast one ply of barrier fibers about the composite structure adjacentto the first endplate of the composite structure forming tool, andwrapping at least one fiber tow about the barrier fibers.

Embodiments herein also generally relate to methods for fabricatingcomposite structures with flanges having tethered corners comprisingproviding a composite structure forming tool including a first endplateand a second endplate and having a composite structure formedthereabout, applying at least one ply of barrier fibers about thecomposite structure adjacent to the first endplate of the compositestructure forming tool, wrapping at least one fiber tow about thebarrier fibers, applying at least one ply of filler fibers over thefiber tow and applying at least one ply of flange fibers over the fillerfibers to obtain a flange preform.

These and other features, aspects and advantages will become evident tothose skilled in the art from the following disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the invention, it is believed that theembodiments set forth herein will be better understood from thefollowing description in conjunction with the accompanying figures, inwhich like reference numerals identify like elements.

FIG. 1 is a schematic perspective view of one embodiment of a fan casinghaving end flanges and a mounting flange;

FIG. 2 is a schematic end view of FIG. 1;

FIG. 3 is a schematic perspective view of one embodiment of a compositestructure forming tool;

FIG. 4 is a schematic cross-sectional view of FIG. 2 along line A-A; and

FIG. 5 is a schematic cross-sectional view of one embodiment of a fancasing with a guide for fabricating a mounting flange having tetheredcorners.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments described herein generally relate to methods for fabricatingcomposite structures with flanges having tethered corners that can helpeliminate the occurrence of bridging during flange layup and cure. Whileembodiments herein may generally focus on composite flanges on fancasings of gas turbine engines, it will be understood by those skilledin the art that the description should not be limited to such. Indeed,as the following description explains, the tethered flange cornersdescribed herein may be utilized on any flange fabricated from compositematerials.

Turning to the figures, FIG. 1 illustrates one embodiment of anacceptable composite structure 10. As used herein, “composite structure”refers to any component fabricated from a composite material orcombination of composite materials. Composite structure 10 may comprisea generally cylindrical member, such as fan casing 12. Fan casing 12 mayhave a circumference, as shown in FIG. 2, and as previously mentionedmay be fabricated from any acceptable material. In one embodiment,however, fan casing 12 may be fabricated from a material selected fromthe group consisting of glass fibers, graphite fibers, carbon fibers,ceramic fibers, aromatic polyamide fibers such aspoly(p-phenylenetherephtalamide) fibers (i.e. KEVLAR®), and combinationsthereof. In one embodiment, fan casing 12 may be fabricated from carbonfibers.

As shown in FIG. 1, fan casing 12 may generally comprise a cylindricalbody 14 having a forward end 16 and an aft end 18. As used herein, “fancasing” is used to refer to both pre- and post-cure composite fancasings. Those skilled in the art will understand which stage is beingreferenced from the present description. Fan casing 12 may also compriseany number of end flanges 20, as shown generally in FIGS. 1 and 2,and/or mounting flanges 22, as shown generally in FIG. 1. As usedherein, “mounting flange” refers to any flange interposedcircumferentially about body 14 of fan casing 12, or other compositestructure. By “interposed” it is meant that mounting flange 22 may belocated circumferentially about body 14 of fan casing 12, as opposed toabout either of forward end 16 or aft end 18. In contrast, end flange 20may be located about either or both of forward end 16 or aft end 18.

Fan casing 12 may be fabricated using any acceptable fabrication methodor tooling known to those skilled in the art. See, for example, U.S.Patent Application Nos. 2006/0201135 to Xie et al., and 2006/0134251 toBlanton et al. In one embodiment, as shown in FIG. 3, a compositestructure forming tool 24 may be used, which has a circumference, agenerally cylindrically shaped core 26, as well as a first endplate 28and a second endplate 30 that may be removeably coupled to core 26 oftool 24.

In FIG. 4 an illustrative embodiment of an end flange preform 32 isshown on fan casing 12. It will be understood by those skilled in theart that the following flange and lay-up descriptions may be equallyapplicable to mounting flanges. End flange preform 32 may include atethered flange corner 33 which can help anchor flange preform 32 inplace during layup and cure. Tethered flange corner 33 may comprise atleast one ply of barrier fibers 34 and at least one fiber tow 36 wrappedcircumferentially thereabout, as described herein below.

More specifically, tethered flange corner 33 may generally include atleast one ply of barrier fibers 34 applied adjacent to first endplate 28of tool 24 and fan casing 12, for example. Barrier fibers 34 may becomprised of multidirectional textile performs such as weaves or braids.As used herein, “multidirectional” refers to textile preforms comprisingfiber tows oriented in more than one direction. Fiber tows of barrierfibers 34 may be comprised of any suitable reinforcing fiber known tothose skilled in the art, including, but not limited to, glass fibers,graphite fibers, carbon fibers, ceramic fibers, aromatic polyamidefibers, and combinations thereof. In one embodiment, barrier fibers 34may be comprised of glass fibers. Additionally, each fiber tow ofbarrier fibers 34 may comprise from about 3000 to about 24,000 fiberfilaments.

Barrier fibers 34 may be applied in flange corner 37 adjacent to firstendplate 28 of tool 24 and fan casing 12 by wrapping barrier fibers 34circumferentially about tool 24 and fan casing 12 until the desiredthickness is obtained. If so desired, barrier fibers 34 may be tackifiedinitially and upon completion of application to fan casing 12 to holdbarrier fibers 34 in place. Any acceptable resin known to those skilledin the art may be used to tackify barrier fibers 34, such as epoxy, forexample.

Next, at least one individual fiber tow 36 may be wrappedcircumferentially about fan casing 12 over barrier fibers 34 in flangecorner 37. In this way, fiber tow 36 can complete tethered flange corner33 and help secure barrier fibers 34 in the desired location. Whilefiber tow 36 may be wrapped about the circumference of fan casing 12 anynumber of times, in one embodiment, fiber tow 36 may be wrapped fromabout 3 to about 6 times about the circumference of fan casing 12.Alternately, more than one fiber tow 36 may be wrapped about fan casing12 one or more times to achieve the same result. Fiber tow 36 may befabricated from any acceptable material known to those skilled in theart including, but not limited to glass fibers, graphite fibers, carbonfibers, ceramic fibers, aromatic polyamide fibers, and combinationsthereof However, in one embodiment, fiber tow 36 may be fabricated fromcarbon fibers. Additionally, each fiber tow 36 utilized may comprisefrom about 3000 to about 24,000 fiber filaments, and in one embodimentabout 12,000 fiber filaments. Once fiber tow 36 is securely wrappedabout barrier fibers 34 of tethered flange corner 33 it may be tackifiedusing any acceptable resin known to those skilled in the art, forexample, epoxy, to hold it in place during the fabrication of theremainder of end flange preform 32.

At least one ply of filler fibers 38 may then be applied over fiber tow36 to help fill in any space that may be present between tethered flangecorner 33 and the flange fibers that will be subsequently applied.Similar to barrier fibers 34, a ply of filler fibers 38 may be amultidirectional textile preform comprised of any suitable reinforcingfiber known to those skilled in the art, including, but not limited to,glass fibers, graphite fibers, carbon fibers, ceramic fibers, aromaticpolyamide fibers, and combinations thereof. Also similar to barrierfibers 34, filler fibers may be wrapped about the circumference of fancasing 12, adjacent to first endplate 28 and over barrier fibers 34 andfiber tow 36 until the desired thickness is obtained. If necessary,filler fibers 38 may be tackified using any acceptable resin known tothose skilled in the art to help hold filler fibers 38 in placethroughout the rest of the fabrication process.

Flange fibers 40 may then be applied over filler fibers 38 using anyknown flange fabrication method known in the art to complete fabricationof end flange preform 32. Once again, flange fibers may comprise anysuitable material such as glass fibers, graphite fibers, carbon fibers,ceramic fibers, aromatic polyamide fibers, and combinations thereof thatcan be wound about tool 24 over filler fibers 38.

To consolidate end flange preform 32, a debulking step may be performed.In particular, reinforcing fibers, such as barrier fibers 34, fillerfibers 38 and flange fibers 40 may inherently have a substantial amountof bulk. In order to help prevent wrinkles and/or voids during the finalcure of the material, and to utilize near net shape tooling during thefinal cure, the fibers of the material can be consolidated, orcompressed, into a dimension that is closer to the desired final curedthickness. This consolidation occurs during debulk.

Debulk can be carried out using any common method known to those skilledin the art, such as, for example, by applying pressure to the compositefibers with either a vacuum bag, shrink tape, or other mechanical means.Resin applied to the fibers before debulk can help tack, or lock, thefibers in place once the pressure is applied. If the tackified fiberscannot be consolidated as desired at room temperature, then heat may beapplied to lower the viscosity of the resin. The resin may then betterinfiltrate the composite fibers and allowing the consolidation to becarried out to the desired degree.

Having finished laying up and debulking end flange preform 32, finalcure tooling can be placed about fan casing 12, including any end flangeperforms and mounting flange performs, to serve as a mold during thecuring process. As will be understood by those skilled in the art, thefinal cure tooling and process may vary according to such factors asresin used, part geometry, and equipment capability.

As previously described, the foregoing is equally applicable to mountingflanges as well as end flanges. When fabricating a mounting flangepreform 41, which is located about the body of fan casing 12, a guide 42may be used in place of first or second endplate to provide a surfaceagainst which to apply barrier fibers 34 and fiber tow 36, as showngenerally in FIG. 5. In one embodiment, guide 42 may be comprised ofdiscrete arcuate members, each spanning about 180 degrees so as to fitcorrespondingly about fan casing 12. The arcs of guide 42 may bereleaseably connected together for easy placement and adjustment aboutfan casing 12. It will be understood, however, that guide 42 may becomprised of any number of pieces and have any shape that corresponds tothe shape of the composite structure. As previously discussed, guide 42can serve as a support for the application of both barrier fibers 34 andfiber tow 36, as well as the remaining fiber layers of the flangepreform 41. Guide 42 may be circumferential and have an L-shapedcross-section as shown, and may be constructed from any rigid,lightweight material such as, for example, aluminum or composite. Onceone side of mounting flange preform 41 is constructed, as shown in FIG.5, guide 42 may be removed. The other side of mounting flange preform 41may then be constructed in the same manner as the first side.

Embodiments of the tethered corner described herein can provide severalbenefits. For example, applying the fiber tow about the barrier fibersallows the fiber tow to serve as a tether to hold the barrier fibers inthe corner of the flange during subsequent lay-up steps. Morespecifically, as additional plies of filler fibers and/or flange fibersare placed and jostled, the barrier fibers stay tethered in the cornerbecause of the wrapped fiber tow. This can help reduce or even eliminatethe bridging issue often faced in current flange fabrication processes.

Additionally, during curing, the composite structure forming toolendplate and core have a tendency to expand and pull away from oneanother due to the heat and pressure of the curing process. This in turncan cause the barrier fibers to be pulled out of the corner and resultin bridging. The tethered corner created by the fiber tow can helpaddress this issue in two ways. First, the tethered corner can reducethe occurrence of bridging in the first instance by helping to hold thebarrier fibers taught. Second, during the curing process, the previouslydescribed expansion of the composite structure forming tool can tightenthe fiber tow of the tethered corner, thereby effectively pulling it andthe barrier fibers against one another in the desired orientation andreinforcing the adhesion therebetween.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to make and use the invention. The patentable scope of the inventionis defined by the claims, and may include other examples that occur tothose skilled in the art. Such other examples are intended to be withinthe scope of the claims if they have structural elements that do notdiffer from the literal language of the claims, or if they includeequivalent structural elements with insubstantial differences from theliteral language of the claims.

1. A method for fabricating a composite structure with a flange having atethered corner comprising: providing a composite structure forming toolincluding a first endplate and a second endplate and having a compositestructure formed thereabout; applying at least one ply of barrier fibersabout the composite structure adjacent to the first endplate of thecomposite structure forming tool; and wrapping at least one fiber towabout the barrier fibers.
 2. The method of claim 1 wherein the barrierfibers are comprised of a material selected from the group consisting ofglass fibers, graphite fibers, carbon fibers, ceramic fibers, aromaticpolyamide fibers, and combinations thereof.
 3. The method of claim 1wherein the fiber tow is comprised of a material selected from the groupconsisting of glass fibers, graphite fibers, carbon fibers, ceramicfibers, aromatic polyamide fibers, and combinations thereof.
 4. Themethod of claim 1 wherein the composite structure has a circumferenceand the barrier fibers are wrapped about the circumference of thecomposite structure adjacent to the first endplate of the compositestructure forming tool to form a flange corner.
 5. The method of claim 4wherein the fiber tow is wrapped about the barrier fibers in the flangecorner.
 6. The method of claim 1 wherein the composite structure is agas turbine engine fan casing.
 7. The method of claim 1 wherein theflange is selected from the group consisting of end flanges, mountingflanges and combinations thereof.
 8. The method of claim 1 wherein thebarrier fibers comprise glass fibers.
 9. The method of claim 1 whereinthe fiber tow comprises carbon fiber.
 10. The method of claim 1 whereinthe fiber tow is wrapped about the barrier fibers from 3 to 6 times. 11.The method of claim 1 wherein more than one fiber tow is wrapped aboutthe barrier fibers.
 12. A method for fabricating a composite structurewith a flange having a tethered corner comprising: providing a compositestructure forming tool including a first endplate and a second endplateand having a composite structure formed thereabout; applying at leastone ply of barrier fibers about the composite structure adjacent to thefirst endplate of the composite structure forming tool; wrapping atleast one fiber tow about the barrier fibers; applying at least one plyof filler fibers over the fiber tow; and applying at least one ply offlange fibers over the filler fibers to obtain a flange preform.
 13. Themethod of claim 12 wherein the barrier fibers are comprised of amaterial selected from the group consisting of glass fibers, graphitefibers, carbon fibers, ceramic fibers, aromatic polyamide fibers, andcombinations thereof.
 14. The method of claim 12 wherein the fiber towis comprised of a material selected from the group consisting of glassfibers, graphite fibers, carbon fibers, ceramic fibers, aromaticpolyamide fibers, and combinations thereof.
 15. The method of claim 12wherein the composite structure has a circumference and the barrierfibers are wrapped about the circumference of the composite structureadjacent to the first endplate of the composite structure forming toolto form a flange corner.
 16. The method of claim 15 wherein the fibertow is wrapped about the barrier fibers in the flange corner.
 17. Themethod of claim 12 wherein the composite structure is a gas turbineengine fan casing.
 18. The method of claim 12 wherein more than onefiber tow is wrapped about the barrier fibers.
 19. The method of claim12 further comprising curing the flange preform to obtain a flangehaving a tethered corner.
 20. The method of claim 12 wherein the flangeis selected from the group consisting of end flanges, mounting flangesand combinations thereof.